1. Field of the Invention
The present invention relates to a method and an apparatus for carrying out image processing that adjusts sharpness of an input image. The present invention also relates to a computer-readable recording medium storing a program that causes a computer to execute the method.
2. Description of the Related Art
There are known image processing methods for emphasizing outlines of subjects in photograph images and for correcting out-of-focus blurs therein, by adjusting sharpness thereof.
For example, a method for obtaining processed image data after carrying out enhancement/reduction processing is known (see U.S. Pat. No. 5,739,922). In the enhancement/reduction processing of this method, image data are decomposed into low frequency components, medium frequency components, and high frequency components, and the high frequency components affecting sharpness of a reproduced image are enhanced while the medium frequency components representing film graininess appearing as granularity in the reproduced image are suppressed. The frequency components after the processing and the low frequency components are combined to generate the processed image data.
However, the sharpness enhancement processing described in U.S. Pat. No. 5,739,922 is realized by enhancing only the specific frequency components, and is not carried out by recognizing main subjects in images. Consequently, a degree of sharpness enhancement is not necessarily optimal therefor. For example, in the case where high frequency components as a target of sharpness enhancement processing include frequency components of edges in the background which is blurrier than a main subject while the degree of sharpness enhancement is determined based on the frequency components of the edges in the background, the sharpness of faces becomes too enhanced as a result of the processing.